With the arrival of the age of multimedia including Internet, further advance as well as globalization of service is required of an optical communication network technology for the basic communication system, and rapid progress in development is being made towards the information society. Further, a receive-function having higher performance is required of a receiver of an optical transmission system as progress towards larger capacity/higher speed of the optical communication circuit advances.
FIG. 3 is a circuit block diagram showing the principal parts of a conventional optical communication module. In FIG. 3, a PD 1 has a cathode connected to a power source V1, and an anode connected to an input terminal of a TIA (Trans Impedance Amplifier) 2.
The TIA2 functions as a differential amplifier, having two output terminals connected to input terminals of a limiting amplifier 4 via capacitors 3a, 3b, respectively. Differential outputs from the limiting amplifier 4 are transmitted to a control circuit (not shown) disposed in a subsequent stage via capacitors 3c, 3d, respectively.
In a configuration as described above, an optical signal inputted is converted into an electric signal by the PD1 to be amplified by the TIA2 in a subsequent stage. At this point in time, outputs from the TIA2 are turned into AC outputs. A DB (data buffer) 4 in a subsequent stage functions as the limiting amplifier as well as a comparator, amplifying the AC outputs from the TIA2 to thereby compare the AC outputs as amplified with a predetermined threshold value, and outputting bit “1” when the optical signal is present while outputting bit “0” when no optical signal is present.
The related art having a configuration where outputs from a PD are amplified by use of a TIA is disclosed in the following Patent Document.    [Patent Document 1] JP 2004-47822 A            JP 2005-62879 A        